1. Field of the Invention
The present invention relates to an antenna, particularly a compact antenna suitable for inclusion in various devices having capabilities for processing radio signals, including various communication devices that can transmit and receive radio signals.
2. Description of the Related Art
In recent years, there have been increasing uses for antennas that can be used in frequency regions in a range of several hundreds of MHz to several tens of GHz due to increasing demand for various devices having capabilities for transmitting and receiving radio signals, including various communication devices for processing radio signals. Obvious uses for such antennas include mobile communications, next generation traffic management systems, non-contacting type cards for automatic toll collection systems, but in addition, because of the trend toward the use of wireless data handling systems that enable to handle data, without using cumbersome lengthy cables, such as cordless operation of household appliances through the Internet, Intranet radio LAN, Bluetooth and the like, it is anticipated that the use of such antennas will also be widespread in similar fields. Furthermore, such antennas are used in various systems for wireless data handling from various terminals, and the demand is also increasing for applications in telemetering for monitoring information on water pipes, natural gas pipelines and other safety management systems and POS (point-of-sale) terminals in financial systems. Other applications are beginning to emerge over a wide field of commerce including household appliances such as TV that can be made portable by satellite broadcasting as well as vending machines.
To date, such antennas described above used in various devices having capabilities for receiving and transmitting radio signals are mainly monopole antennas attached to the casing of a device. Also known are helical antennas that protrude slightly to the exterior of the casing.
However, in the case of monopole antennas, it is necessary to extend the structure for each use of the device to make the operation cumbersome, and, there is a further problem that the extended portion is susceptible to breaking. Also, in the case of the helical antennas, because a hollow coil that serves as the antenna main body is embedded in a covering material such as polymer resin for protection, the size of device tends to increase if it is mounted on the outside the casing and it is difficult to avoid the problem that the aesthetics suffers. Nevertheless, reducing the size of the antenna leads only to lowering of signal gain, which inevitably leads to increasing the circuit size for processing radio signals to result in significantly higher power consumption and a need for increasing the size of the battery, and ultimately leading back to the problem that the overall size of the device cannot be reduced.
On the other hand, when attempts are made to realize a high gain compact antenna comprised by resonance circuit having an inductance section and a capacitance section to transmit and receive radio waves, it is not sufficient to provide only one resonance section because of insufficient gain produced by such a design, and therefore, it is necessary to combine a plurality of resonance sections to produce one antenna working as a whole. However, if the gain in individual resonance sections is increased, the widths of the characteristic resonance curves become narrow, and a problem arises that it is not possible to resonate all the resonance sections at one frequency in nearly the same phase. Conversely, if the resonance widths are made wider so as to resonate all the resonance section at one frequency in nearly the same phase, it gives rise to a problems that Q values decrease, and consequently, sufficient gain cannot be obtained.
Particularly, when the size of the antenna is made smaller, variations in the inductance and capacitance values tend to increase, causing the individual resonance frequencies to differ to the extent that the widths of the resonance curves hardly superimpose. In practice, it is difficult at the present time to resonate a plurality of resonance sections at one frequency in nearly the same phase while obtaining sufficient gain in individual resonance sections. Even if it is supposed that production is possible with sufficient precision, the productivity inevitably suffers so that there has been a need to develop a new technology to resolve such problems.
The present invention is provided in view of the background information described above, and an object is to provide a compact antenna that can produce high gain.
The antenna according to the present invention is an antenna comprised by an antenna main body having a plurality of resonance sections connected electrically in series, wherein each resonance section has an inductance section and a capacitance section connected electrically in parallel and resonates at an normal vibration frequency; and the plurality of resonance sections are constructed in such a way that characteristic frequency curves overlap one another at least in the width portion of respective curves so that each resonance section resonates at nearly the same normal vibration frequency, and the antenna main body is constructed so as to have at least one resonance frequency different from the normal vibration frequency of the resonance sections which is produced by coupling of the individual resonance sections.
Furthermore, it is preferable that the resonance frequency is used as a center frequency for transmitting or receiving radio waves for the antenna.
In this case, it is preferable that the center frequency is selected to be higher than the normal vibration frequency.
Especially, it is preferable that the antenna is constructed so that the center frequency is higher than twice the normal vibration frequency.
Therefore, it is preferable that a frequency adjusting capacitance section is connected electrically in series to the antenna main body for adjusting the resonance frequency.
Particularly, it is preferable that the frequency adjusting capacitance section is mounted between the exit end of the antenna main body, which is opposite to the feed end, and a ground section connected to ground potential.
Especially, it is preferable that the ground section is connected electrically from the exit end of the antenna main body to a ground-side of a power line that supplies power to the antenna main body.
According to the present invention, by constructing the antenna in such a way that the antenna main body can resonate at the resonance frequency different from the characteristic individual normal vibration frequencies of the resonance sections, the resonance frequency different from the normal vibration frequency can be selected as the center frequency to be used for radio wave transmission and reception, thereby improving the antenna performance from the viewpoint of releasing the radiative energy from the resonance sections. The reason is that, if the normal vibration frequency itself is chosen as the center frequency, it is thought that a type of energy storage section, in which a current amounting to Q times the current flowing in the antenna main body is flowing, is created in the interior of the resonance sections (acting as a parallel resonance system), to impede the transfer of electromagnetic energy. Therefore, by selecting the center frequency different from the normal vibration frequency, the energy release is facilitated from the capacitance section connected to the inductance section in parallel, thus increasing the antenna gain.
From this viewpoint, the normal vibration frequency at which the resonance section resonates may be higher or lower than the center frequency for reception or transmission of radio waves, but it is preferable that the normal vibration frequency is selected from the low-frequency-side of the center frequency. This is due to the fact that, if the normal vibration frequency is made lower, high values can be chosen for the inductance sections and capacitance sections so that the gain is increased. In other words, if the sizes for the inductance sections and capacitance sections are chosen so as to resonate in the low-frequency-side of the center frequency, it is more desirable for increasing the gain, because the opening area of the coil sections would become relatively larger for short wavelengths of the electromagnetic waves at the center frequency in the high frequency region, for example, and enhanced performance of the antenna may be expected.
For this reason, by choosing a high value of the center frequency, especially if it is higher than twice the normal vibration frequency, phase-matching is further facilitated for the resonance sections, thus enabling to obtain high gain.
Here, it is preferable, in stabilizing the resonance frequency for the overall antenna main body, to connect one end of the frequency adjusting capacitance section in series to the antenna main body and connect other end of the frequency adjusting capacitance section to the ground section at the ground potential. In the first place, the antenna main body cooperates with the ground section and others to resonate as an overall resonating body to generate the resonance frequency different from the normal vibration frequencies of the resonance sections, and therefore, it is possible to adjust the resonance frequency to the center frequency with the frequency adjusting capacitance section. While normal helical antennas, a floating capacitance is generated between the helical body of the helical antenna and the grounded plate, to make the resonance structure vulnerable to adverse effects from the surrounding environment, the present frequency adjusting capacitance section has a specific fixed value, thus enabling to eliminate causes for instability such as adverse effects of surrounding environment.
Also, the inductance section of the antenna main body has coil sections comprised by a conductor formed in a spiral-shape or an angular shape that can be approximated by a spiral.
In this case, it is preferable that the coil axes of the coil sections are aligned substantially on a straight line.
Also, at least one portion of the conductor that circles the coil axes of the conductor sections is contained in a plane inclined at an angle to the coil axes.
Further, the resonance section is constructed by connecting two resonance sections electrically in series.
By adopting such a structure, it is possible to increase the antenna gain. This is due to the fact that, the gain tends to be lower compared with an antenna having two resonance sections, although more than three resonance sections may be connected in series.
Another embodiment of the present invention relates to an antenna comprised by an antenna main body containing a plurality of resonance sections connected electrically in series and receives power from a feed end, wherein each resonance section has an inductance section and a capacitance section connected electrically in parallel and resonates at an normal vibration frequency; and a ground section connected to the ground potential; and the plurality of resonance sections are constructed so that the characteristic frequency curves overlap one another at least partially in the width potion of the respective curves so as to enable the plurality of resonance sections to resonate at nearly the same normal vibration frequency; and the antenna main body is constructed so that the antenna main body has at least one resonance frequency different from the normal vibration frequency produced by coupling of individual resonance sections so that the one resonance frequency is used as a central frequency for transmitting or receiving radio waves for the antenna.
In this case, it is preferable that the frequency adjusting capacitance section is mounted between the exit end, which is opposite to the feed end of the antenna main body, and the ground section.
Especially, it is preferable that the center frequency is higher than the normal vibration frequency, and in particular, the center frequency is higher than twice the normal vibration frequency.
Also, the ground section may be connected electrically to a ground-side of the power line that supplies power to the antenna main body through the feed end of the antenna main body.
Still another embodiment of the present invention relates to an antenna comprised by a plurality of resonance sections having an inductance section and a capacitance section connected electrically in parallel and resonating at a normal vibration frequency; and an antenna main body having the plurality of resonance sections connected electrically in series, each resonance section in the plurality of resonance sections is constructed so that the characteristic frequency curves overlap one another at least partially in the width potion of the respective curves so as to enable each resonance section in the plurality of resonance sections to resonate at frequencies substantially identical to the normal vibration frequency, and the antenna main body has at least one resonance frequency, higher than the normal vibration frequency, as a result of coupling of individual resonance sections.
In the present invention, for example, inductance value of the inductance section that comprises the resonance section is made high and capacitance value of the capacitance section that comprises the resonance section is made low so as to increase the resonance width of the characteristic frequency curves, and therefore, a frequency region included in the resonance width of any resonance section emerges, so that the characteristic frequency curves can overlap at least partially in the width portion of the respective curves. The resonance sections resonate substantially in-phase at one frequency close to the individual normal vibration frequencies within the frequency region where the characteristic frequency curves overlap. Therefore, when these resonance sections are connected electrically in series, the antenna main body responds in such a way that the individual resonance sections couple with one another to produce one resonance frequency that corresponds to the normal vibration frequency, and furthermore, resonance frequencies are generated in a higher frequency region than the normal vibration frequency. It is true that, in order to align the phases of vibration of individual resonance sections, the widths of the normal vibration frequencies are increased and the Q-factors are lowered, nevertheless, in relation to the low-frequency-side, the Q-factor in the high-frequency-side has been increased so that sufficient gain is obtained for the resonance frequencies in the high frequency region.
Accordingly, by constructing the antenna in such a way that the individual resonance sections vibrate in-phase at resonance frequencies on the low-frequency-side of the center frequency, high gain is obtained at the resonance frequencies in the high-frequency-side.
It is preferable that the resonance frequency higher than the normal vibration frequency is used as a center frequency for transmitting and receiving radio waves.
By adopting such a structure, radio waves are transmitted or received using the resonance frequency in the high-frequency-side of the normal vibration frequency of the individual resonance sections. The present antenna thus enables to produce a higher gain than the resonance gain in the low-frequency-side.
The present invention relates also to a radio wave transmission reception apparatus having a transceiver antenna for transmitting or receiving radio waves using an operational center frequency, wherein the transceiver antenna described in any one of the examples described above is used, and the center frequency is used as the operational center frequency.
By adopting such a structure, a compact transceiver antenna of high gain is realized, and the overall size of a radio wave transmitting and receiving apparatus is reduced.
The present invention relates also to an antenna main body receiving power from a feed end through a power line and operates in cooperation with a ground section connected to a ground-side of the power line to transmit or receive radio waves, wherein the antenna main body is comprised by a plurality of resonance sections having an inductance section and a capacitance section connected electrically in parallel and resonating at a normal vibration frequency, and the plurality of resonance sections are connected electrically in series, and each of the plurality of resonance sections is constructed so that the characteristic frequency curves overlap one another at least partially in the width portion of the respective curves so as to enable each resonance section in the plurality of resonance sections to resonate at frequencies substantially identical to the normal vibration frequency, to generate at least one resonance frequency, different from the normal vibration frequency, as a result of coupling of individual resonance sections, and one of the resonance frequencies is used as a center frequency to transmit or receive radio waves.
In this case, it is preferable that the center frequency is a frequency that is higher than the normal vibration frequency.
The present invention relates also to a method for making an antenna by fabricating a plurality of resonance sections, wherein each resonance section resonating at a normal vibration frequency is made by connecting inductance section and capacitance section electrically in parallel so that the characteristic frequency curves overlap one another at least partially in the width portion of the respective curves so that the plurality of resonance sections resonate at nearly the same normal vibration frequency; then, fabricating an antenna main body by connecting the plurality of resonance sections electrically in series so as to produce the antenna main body having at least one resonance frequency of higher frequency than the normal vibration frequency; and adjusting one of the resonance frequencies by connecting a frequency adjusting capacitance section electrically in series to match one of the resonance frequencies, having a higher frequency than the normal vibration frequency, to the operational center frequency for transmitting or receiving radio waves.
In the present invention, in the resonance section fabrication process, inductance value for the inductance section is chosen high, and capacitance value for the capacitance section is chosen low so as to increase the width of the characteristic resonance curves. When the resonance circuit is so designed, there emerges a frequency region which can be included in the width portion of any resonance curves of the resonance sections. In such a circuit, the characteristic frequency curves overlap at least partially in the width portion of the respective curves. Then, the resonance sections resonate substantially in-phase at one frequency close to the individual normal vibration frequencies within the frequency region where the characteristic frequency curves overlap. Therefore, when these resonance sections are connected electrically in series in the antenna main body fabrication process, the antenna main body produces a resonance frequency that corresponds to the normal vibration frequency generated by coupling of the individual resonance sections, and furthermore, resonance frequencies are synthesized in a higher frequency region than the normal vibration frequency. It is true that, in order to align the phases of vibration of individual resonance sections, the widths of the normal vibration frequencies are increased and the Q-factors are lowered, nevertheless, in comparison to the low-frequency-side, the Q-factor of the high-frequency-side has been increased so that sufficient resonance gain is obtained in the high frequency region. Further, in the frequency adjusting process, by connecting a frequency adjusting capacitance section electrically in series to the antenna main body, and adjusting the resonance frequency that has a frequency higher than the normal vibration frequency to match the center frequency, radio waves can be transmitted or received at a higher gain than that possible in the low-frequency-side of the center frequency.
The effects of the present antenna are summarized below.
An antenna according to the present invention is comprised by an antenna main body having a plurality of resonance sections connected electrically in series, wherein each resonance section has an inductance section and a capacitance section connected electrically in parallel; and each resonance section in the plurality of resonance sections is constructed so that characteristic frequency curves overlap one another at least partially in the width portion of respective curves, so that resonance sections resonate at frequencies substantially identical to the normal vibration frequency, and the antenna main body is constructed so as to have at least one resonance frequency that is different from the normal vibration frequency produced as a result of coupling of the resonance sections, thereby enabling to increase the antenna gain.
Also, since one of the resonance frequencies is adjusted to the center frequency for transmitting or receiving radio waves for the antenna, it becomes possible to transmit and receive radio waves with a high gain.
Also, according to the present invention, because the center frequency is higher than the normal vibration frequency, and especially, the center frequency is higher than twice the normal vibration frequency, the antenna gain is increased.
Also, according to the present invention, because the frequency adjusting capacitance section is connected electrically in series to the antenna main body, the antenna can be made to resonate at the resonance frequency different from the normal vibration frequency and the frequency of the synthesized resonance can be adjusted, thereby enabling to increase the antenna gain.
Also, according to the present invention, because the frequency adjusting capacitance section is mounted between the exit end, which is opposite to the feed end of the antenna main body, and the ground section connected to the ground potential, the antenna main body cooperates with the ground section, and the antenna as a whole resonates at a resonance frequency different from the normal vibration frequency, thereby enabling to adjust the overall resonance frequency to a desired center frequency by changing the value of the capacitance of the frequency adjusting capacitance section.
Also, according to the present invention, because the inductance section of the antenna main body has coil sections comprised by a conductor formed in a spiral-shape or an angular shape that can be approximated by a spiral, and the axes of the coil sections are aligned substantially on a straight line, and at least one portion of the conductor that circles the coil axes of the conductor sections is contained in a plane inclined at an angle to the coil axes, the antenna gain is increased.
Also, according to the present invention, because the resonance means is constructed in such a way that two resonance sections are connected electrically in series, antenna gain can be increased.
Also, according to the present invention, because the antenna of the present invention is used as the transceiver antenna in a radio wave transmission and reception apparatus for transmitting or receiving radio waves, the transceiver antenna is compact and produces high gain so that the overall size of the radio wave transmission and reception apparatus can be made small.
Also, according to the present invention, a method is provided for making an antenna comprised by: a resonance section fabrication process for fabricating a plurality of resonance sections in which each resonance section is made by connecting inductance section and capacitance section electrically in parallel so that the plurality of resonance sections resonate at frequencies substantially identical to the normal vibration frequency; followed by an antenna main body fabrication process for connecting the plurality of resonance sections electrically in series so as to produce the antenna main body having at least one resonance frequency higher than the normal vibration frequency; followed by a resonance frequency adjusting process for connecting a frequency adjusting capacitance section electrically in series to the antenna main body and adjusting one of the resonance frequencies having a higher frequency than the normal vibration frequency to match the center frequency for transmitting or receiving radio waves. Therefore, a plurality of resonance sections can be made to vibrate in-phase at a resonance frequency in the low-frequency-side so that high gain can be obtained at a resonance frequency in the high-frequency-side of the normal vibration frequency. Thus, it enables to transmit or receive radio waves at a higher gain than the resonance gain in the low-frequency-side.